Process of purifying bodies insoluble in water



Patented a. 4, 1932 UNITED sures;

PATENT OFFICE JOHN KEARSLEY "MITCHELL, 0F VILLANOVA, PENNSYLVANIA,ASSIGNOR T0 DISPERSIONSN'PROQESS, INQ, OF DOVER, DELAWARE, A CORPORATIONOF DELA- WARE i yrnocnss on mmmm nomns INTSOLUBLE IN WATER No Drawing.

There are various solid bodies, and more I gum industry,rwhereiti isessential that the 50. rubber or gum base be 9f; high purity, it hasorganic class, which areinsolublegin water i and so cannotbe purified bydissolving them to form an aqueous solution and then precipitating orcrystallizing them from solution. Some of these bodies are liquefiableby heat and may be purified in hot liquid condition 7 by filtration, butthere are some bodies which undergo decomposition when heated, and socannot be purified by this method. For instance,\there is a large classof bodies which may be generally termed ,rubbers orfgums, which areinsoluble in water and whichcansiderable difficulty andexpense. Most ofthe wild rubbers, including those which are vulcanizable'and knownastrue I rubbersand those which are non-vulcanizable, such as theguttas,are gathered and coagulated by natives who .pay little attention to thecleanliness of their product Some natives haveeven been. known tointroduce bark andother foreign materialsinto the rubber to increase itsapparent weight. So, too, when rubber is extracted from shrubs or thelikeyit is usually contaminated with fi- I brous material and" otherimpurities;

field before shipment, usually appears on the market associated withimpurities and must again be washed before manufacture into rub- 1persing agent 1s water-soluble, so that when her goods. The presence ofeven a smal amount of coarse impurities in the rubber is usuallyobjectionable, as these may appear in the finished goods and render themdefective. It is generally the custom to, wash rubber by. working itbetween "a pair of corrugated rolls rotatingat different speeds, andplaying water intothe nip of the-rollsto wash out the impurities thusbrought tothe surface. The

cost of'so washing depends-upon the amount:

of impurities present in therubber, and the cleanliness desired'in thefinal product, but

even when such'washing is done.v for a long while, it does not yield aproduct substantially free from impurities. .In. the chewing not beliquefied. The purification of these bodies has therefore been amatter-of con- Wild rubber, even when washed on the Application filedNovember 30,1928. Serial No. 322,954.

been found preferable to wash in a so-called internal mixer of the Dayor, Werner & Pfleiderer type, as such mixers by their kneading andpulling action expose impurities" at a much higher rate than rolls. Butwashing so carried out is also expensive and time-consuming.

In accordance with the present invention, bodiessuch as described, (e.g., wild rubbers such as Para and African rubber, guttas, guayule, orthe like), which are insoluble in water, are dispersed as fine particlesin a liquid medium, impurities associated with such bodies thus becomingsuspended in the dispersion, whereupon the impurities ,may beremoved asby passing the dispersion over screens of sufficiently fine mesh topermit the dispersed particles and liquid medium to pass through whileimpurities remain on the screens. Such a process is especially useful ineffecting the purification of rubber associated with impurities.Therubber may be dispersed by manipulating it in the presence of ahydrophilic colloid and water until it disperses in the aqueous mediumas particles in the order of magnitude of the rubber globules of latex.The dispersion contains the dirt, bark, or other impurities insuspension therein, so that they may be removed by screening, whereuponthe rubber may be coagulated and recovered from the dispersion,

. or, if desired, used in dispersed form. Preferably, the hydrophiliccolloid used as a dis- .base in the manufacture of chewing gum. Therubber used for this latter purpose is usually one of quite high resincontent, as these have been found to have the desired chewable quality.Such resinous rubber may be dispersed in water quite readily, requiringcomparatively little manipulation in the presence-of water andwater-soluble hydrophilic colloid. such as soap, to undergo the desiredchange from the condition of acoherent body in the continuous phase tothat of fine particles in the disperse phase, and.

the rubber may then berecovered from the dispersion as a.coagulum, whichmay be T washed sufficiently free of colloid tohavesub stantially noefiect on its use as a chewing gum base. In fact, in some cases, theremay be a sufiicient' quantity of saponlfia-blematerial, perhaps of. areslnousnature, present 7 in'the rubber or gum to effect its dispersionI upon the additioniiOff-"'Oillys a *spo ni'fyingr agent and water. Aprocedureintendedto yield a productof this character may beca'rried outsubstantially asfollows. A gutta or a mixture of guttas orgumscomp'ounded then be putinto "a suitable manipulating apmixer thenbeing set in operation, While the mixeris in operation,about l'0% byweight offa'soap, such as-fsodium resinate, maybe added and uniformlydisseminated throughout'themass', or may be formed in situ, where-.up'on water may be slowly added and worked into-the mixtureuntil therubber disperses as fine .particles in the aqueous medium. Thedispersion is thus jefiected' without the necessity ofraising thetemperature offthe material to its melting point or to any point 7 whichwould'be likely t o in'jure'or modify the characteristics of the gum orgutta con stituents of themass which remains solid during dispersion. lThe resulting dispersion may have a'solids contentof about &0% and willbe of a 'fiuidityfsuificient 'to permit it to bescreened to removeimpurities suspended,

therein. For'instance,'the dispersion may becaused to flowagain'stscreens, forinstance,

of .the stationary, vibrating, or oscillating type, and 0f any d'esiredfineness,say 300 mesh, the dispersed rubberjand water pass ing throughthe, screens while" impurities re main on the screens. If desired,.theimpurities may be removed in portions ofpro-- gressively decreasingcoarseness, by uslng a succession of screens of successlvely finer' vmesh, say, 80 to 300, mesh. This avoids plugging of, the fine-screens bythe. coarsest im purities. The screeneddispersion is 'characterized byits smoothness; and cleanliness,

and its rubber content WhenfcOagulated is of ektremely fine texture-Coagulation may be'elfeeted by various methods. f Forinstance,

the water, content of the dispersion maybe removed evaporating as bydrum- 301 "spray-,dryingr The'soap present inthecoQ agu1um-may, ifdesired, be readilyr'emoved; by washing on .the usual washing rolls toproduce a substantially pure'produ'ct: Or the .rubber'1 maybe coagulatedfrom the disper sion by "the addition of suitable electrolytes,

such as a solution of calcium chloride or acetic acid,o'r by the use ofany of thewell known coagulating agents, the. coagulumthen be ing washedfree of the' electrolyte and solubleproducts of coagulation,if'desired,by

washing as previously;described, 'Still another methodby. whichcoagulation and Washing may be simultaneously efi'ected is toidilute thedispersion-with a. comparatively.

large amount of water, ,in'rrwhich .case t dispersed rubber particles'coagulate orfco- :here into agglomeratesgwhich are suspended in thedilute aqueous medium and Which-may "be remoyed-by: screening or maybebroughti down as a coherent naSsbyheating, The last method' may be:carried out. in actual practice atgcomparativfelyi"lo-W expense, as

the dispersion may be. added slowly,pas for instance, in the form of aspray, into ailarge body of agitated water,-.whereupon the suspendedrubber agglomerates may beremo'ved by any suitablemethod such asscreening, or

centrifugal I action," and then dried jto pro-I ducefa coherent'mass; ortheagglomerates may be caused to"c'oalesce into a coherent mass, byheating the'suspension of agglomerates'or by maintaining the body ofdiluting water intowhichthediszpersion is being deliveredat elevatedtemperature; Afterd'ry ing, no odor 'or taste of soap can be detected inthe coagulum, as substantially all ofthe soap present in the dispersionremains dissolved in the large quantity of diluting water. necessarytoeffect agglomeration "andcoagulation.- The drycoagulum is eminent: ly'satisfactory for use as a base in the man I ufa'cture of 'chewing gums,as, it maybe directly compounded with sugar, flavor, and

products.

other ingredients customarily used for such '3 While hefor oa tem s hastot-" 1 with the processing'of non-vulcanizable rubbers suitablefforchewing gum manufacture,

vulcaniz'able rubbers. may be similarlyproc essed for use in themanufacture of, rubber goods,but'*in such casefthe colloid 'may-be leftin theresultingproduct; ,If' desired,

the screened rubber dispersion, maybe used 5 as such 1n the manufactureof various products, as, for example, in the impregnation'or coating offabricsor other'fibrousfounda tions: Or the" dispersion maybeinc'o-rpo-;-

rated into fibrous pulp in the .beater' engine, and the rubber.coagulated on the'fibers be fore the pulp is sheeted on 'apaper machineor'otherwisefabricated, or it may be used? such dispersions aresuitable. Y

for any of th-e'many -other purposes forwhich "Hydrophilici colloidsother al sat, such as casein, albumin, colloidal clay, or the like, maybe'successfullyused, soaps, how ever,'be1ng preferable in cases whereit-is desired'to produce a fin alfp'roduct substantially free fromanyadded clolloid. Suchsoaps may be used in prepared-conditionas'described,

like substances associated with impurities or they may be formed insituin the rubber by incorporating thereinto, soap-forming substances, suchas rosin, pine tar, fatty acids or fatty acid glycerides, and thenadding an alkali such as caustic soda to effect saponification.

' Having thus described certain embodi f ments of this invention, itshould be evident to those skilled in the art that various changes andmodifications might 'be made therein without departing from the" spiritor scope of invention as defined by the appended claims. V I

I claim:

1. A process of purifying wild rubber and occurring in'the crudeproduct, which comprises manipulating the rubber in the presence ofwater and a hydrophilic colloid until it disperses as fine solidparticles in the aqueous medium in which the impurities are thensuspended, screenlng the dispersion to remove impurities, addingthescreened dispersion to a body of heated water to coagulate thedispersed rubber, removing the coagulum, and drying. r V

' 2. A process of purifying wild rubber and a like substances associatedwith impurities 0ccurringin the crude product, which comprisesmanipulating the rubber in the presence of water and a water-solublesoap until it disperses as fine solid particles in the aque ous mediumin which the impurities are then suspended, screening the dispersion toremove impurities, and spraying the dispersion into a body ofheated'water under agitation to coagulate the rubber and remove soaptherefrom.

3. A process of purifying wild rubber and like substances associatedwith impurities occurring in the crude product, which comprisesmanipulating the rubber in the presence of water and a water-solublesoap until it dispersesas fine solid particles in the aqueous medium inwhich the impurities are then suspended, screening the dispersion toremove impurities, spraying the dispersion into a body of heated waterunder agitation to coagulate the rubber and remove soap there'- from,removing the rubber coagulum, and drying; o I i In testimony whereofI'have aflixed my signature.

JOHN KEARSLEY MITCHELL.

